Minor cleaning up of the EchoCancellationImpl code
Minor cleaning up of the EchoCancellationImpl code

BUG=

Review URL: https://codereview.webrtc.org/1767043002

Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#11899}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 4510bbd5fcdbb27a7ee86d30ff3ee938dedf95b9

Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,jchavanton/webrtc,Alkalyne/webrtctrunk,jchavanton/webrtc,jchavanton/webrtc,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,jchavanton/webrtc,jchavanton/webrtc,jchavanton/webrtc,jchavanton/webrtc